Controlling the temperature of the exhaust valves is paramount for proper
functioning of engines and for the long lifespan of valve train components. The
majority of the heat outflow from the valve takes place along the valve-seat-cylinder
head-coolant thermal path which is significantly influenced by the thermal contact
resistance (TCR) present at the valve/seat and seat/head interfaces.
A test rig facility and experimental procedure were successfully developed to assess
the effect of the valve/seat and seat/head interfaces on heat outflow from the valve,
in particular the effects of the valve/seat interface geometry, seat insert assembly
method, i.e. press or shrink fit, and seat insert metallic coating on the operating
temperature of the valve.
The results of tests have shown that the degree of the valve-seat geometric
conformity is more significant than the thermal conductivity of the insert: for low
conforming assemblies, the mean valve head temperature recorded during tests on
copper-infiltrated insert seats was higher than that recorded during tests on noninfiltrated
seats of higher conformance.
The effect of the insert-cylinder head assembly method, i.e. shrink-fitted versus
press-fitted inserts, has proved negligible: results have shown insignificant valve
head temperature variations, for both tin-coated and uncoated inserts. On the other
hand, coating the seat inserts with a layer of tin (20-22¿m) reduced the mean valve
head temperature by approximately 15°C as measured during tests on uncoated seats.
The analysis of the valve/seat and seat/head interfaces has indicated that the surface
asperities of the softer metal in contact would undergo plastic deformation. Suitable
thermal contact conductance (TCC) models, available in the public domain, were
used to evaluate the conductance for the valve/seat and seat/cylinder head interfaces.
Finally, a FE thermal model of the test rig has been developed with a view to assess
the quality of the calculated TCC values for the valve/seat and seat/head interfaces.
The results of the thermal analysis have shown that predicted temperatures at chosen
control points agree with those measured during tests on thermometric seats with an
acceptable level of accuracy, proving the effectiveness of the used TCC models.
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/4333 |
| Date | January 2009 |
| Creators | Abdel-Fattah, Yahia |
| Contributors | Rosala, George F., Wright, Steve |
| Publisher | University of Bradford, School of Engineering Design and Technology |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
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